Date: Mon, 14 Nov 2016 21:53:18 -0800 From: Mark Millard <markmi@dsl-only.net> To: Nathan Whitehorn <nwhitehorn@freebsd.org> Cc: "Jukka A. Ukkonen" <jau789@gmail.com>, Justin Hibbits <chmeeedalf@gmail.com>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org>, Peter Grehan <grehan@freebsd.org> Subject: Re: svn commit: r306065 - in head/sys vs. PowerMacs: Nathan's trail patch included but inappropriate? [My hack vs. Apple G4's.] Message-ID: <B28E3336-2F85-4395-8DDF-CF09CA9D41E1@dsl-only.net> In-Reply-To: <01cfa4e9-954f-3e86-c8d7-36ec8523dde0@freebsd.org> References: <C48933C3-DB22-4D94-B22D-B51822197E4E@dsl-only.net> <917EFF5A-D054-4424-9D7D-4E4BEF6072EF@gmail.com> <4bb1046a-225d-66b2-7b00-067f0d6f6c60@gmail.com> <465041D5-C1A2-48F4-9CA7-DD03B094FAE4@dsl-only.net> <01cfa4e9-954f-3e86-c8d7-36ec8523dde0@freebsd.org>
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On 2016-Sep-21, at 3:01 PM, Peter Grehan <grehan at freebsd.org> wrote: >> I've never had my hands on an eMac. I'm not sure if it has the same >> SPRGx requirements as other G4's or not. > > That's the machine that caused the sprg save/restore. > https://svnweb.freebsd.org/base?view=revision&revision=151891 > > later, > > Peter. My patch/hack as I have always had it for booting PowerMac G5's does not change the content for G4's (such as eMac G4's). I made a separate case for __powerpc64__ --and only for AIM-capable as well. My code has been: # svnlite diff /usr/src/sys/powerpc/ofw/ofw_machdep.c Index: /usr/src/sys/powerpc/ofw/ofw_machdep.c =================================================================== --- /usr/src/sys/powerpc/ofw/ofw_machdep.c (revision 308247) +++ /usr/src/sys/powerpc/ofw/ofw_machdep.c (working copy) @@ -111,6 +111,24 @@ * Assume that interrupt are disabled at this point, or * SPRG1-3 could be trashed */ +#if defined(AIM) && defined(__powerpc64__) +/* HACK: PowerMac G5 specific code to avoid demonstrated hangs in + * the early boot time frame: avoid mtsprg0 use. + * This would need a live test for PowerMac vs. not in order + * to remove HACK status --but without calling into + * OpenFirmware or the problem would be recreated. + */ + if (1) + __asm __volatile("mfsprg0 %0\n\t" + "mtsprg1 %1\n\t" + "mtsprg2 %2\n\t" + "mtsprg3 %3\n\t" + : "=&r"(ofw_sprg0_save) + : "r"(ofmsr[2]), + "r"(ofmsr[3]), + "r"(ofmsr[4])); + else +#endif __asm __volatile("mfsprg0 %0\n\t" "mtsprg0 %1\n\t" "mtsprg1 %2\n\t" (The comment does not reflect the modern discussion of why the change works: the code has been around a long time.) I do not know if there are any AIM-capable __powerpc64__ contexts for which the change is inappropriate. It would be nice if it was always appropriate to that kind of context and could be added to head and stable/11 and stable/10 . (I've no experience before stable/10: so untested prior to that.) Jukka did experiments with eliminating more --and not just for AIM-capable __powerpc64__ but some other PowerMac contexts as well. But I kept to the minimal generated-code change which appeared to fix the problematical behavior. === Mark Millard markmi at dsl-only.net
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